Expanded cellular plastic flotation body



Nov. 24, 1953 J. J. HOFFMAN EXPANDED CELLULAR PLASTIC FLOTATION BODY Filed Aug. 9, 1952 l hr I ll Patented Nov. 24, 1953 EXPANDED CELLULAR PLASTIC FLOTATION BODY John J. Hoffman, South Bend, Ind., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application August 9, 1952, Serial No. 303,630

Claims. (Cl. 137452) This invention, relates to a tough, durable fiotation body which is formed of expanded cellular plastic materials in such a manner that the body will not shatter or otherwise lose its buoyancy to any substantial extent when it is subjected to abuse, and in particular it relates to such a flotation body which is designed to withstand such extreme abuse as gun fire without shattering.

Expanded cellular plastic materials consist of myriad small closed gas cells throughout a plastic mass, hence these materials have excellent flotation properties. The term cellular as used herein denotes a closed (nonintercommunicating) cell structure sometimes H termed unicellular (see Gould, Rubber Chemistry and Technology, 17, 943 (1944). Expanded cellular materials can be formed in extremely low densities to have great buoyancy, and, since each cell is effectively a separate flotation cell, the material will not lose its buoyance to any substantial extent when any cell is destroyed. This invention utilizes this property of expanded cellular materials to produce flotation bodies which are suitable for use as buoys, parts of life rafts, boats, etc.

Because of its durability, the flotation body of this invention will find general use in applications such as these, but it is designed for, and will be particularly useful in, these and similar applications when the flotation bodies are to be used during military operations in which they will be subjected to gun fire. Thus, for example, a flotation body according to this invention will be particularly useful as a float which, when fixed interspersed to heavy military equipment such as tanks or-- purpose, but these tanks must be armored, and

when they are pierced they immediately lose their buoyancy.

When flotation bodies are to be used during military operations, it is extremely important that they be able to withstand gun fire without 3 losing their buoyancy. Further, since flotation "bodies which are to be used in thes operations .may be stored for extended periods of time under very adverse conditions before being used, they ,must be constructed of materials which can retain their flotation properties under these storage conditions. Thus the bodies should be vermin proof; they should be chemically resistant to oils and, other hydrocarbons; they should not support combustion; they should be capable of supporting high sustained pressures without crush ing; etc. Further, since it will be used under such adverse conditions that the body may be damaged or destroyed in use, it should be con- 3 structed of readily available materials, so the body is expendable.

The flotation body of this invention possesses all of these qualities, and because it combines these qualities w th great buoyancy and shatterresistance it is, exceptionally well suited for flotation uses of the kind specified.

This invention particularly contemplates a flotation body formed of expanded cellular materials which comprises a relatively large core of readily available expanded cellular plastic material completely enclosed in a relatively thin shell of a tough rather rigid expanded cellular plastic material. The core and shell are combined into a flotation body of great buoyancy which is capable of withstanding extreme abuse, particularly gun fire, without shattering or otherwise losing its buoyancy to any substantial extent.

More specifically this invention contemplates a flotation body comprising a relatively large core of expanded cellular polystyrene resin completely enclosed in a thin shell of a tough rather rigid expanded cellular material selected from the group consisting of plasticized polyvinyl chloride, plasticized resinous copolymers of a major proportion of vinyl chloride and a minor proportion of a copolymerizable monomer, and mixtures of (A) from 50 to per cent of a thermoplastic resin and (B) correspondingly from 50 to 20 per cent of a rubbery material compatible with this resinin which the percentages are based on weight and computed on the sum of the Weights of (A) and (B). The core is formed as a single body, or as a plurality of bodies which are assembled to form the core, and the shell placed about the core to completely enclose it within the shell. The thickness of this thin shell may be varied to some extent, but preferably it is kept in the range of 14 inches, for when a flotation body is made in accordance with this invention having a shell of this thickness it is capable of withstanding .50 calibre and larger gun fire without shattering or crumbling under the impact of the shell. The densities of the core and shell material may also be varied somewhat, but preferably the raw materials are compounded with sufficient quantities of a blowing agent and processed in such a way as to yield a cellular y having a density not greater than 5 lbs. per cubic foot to provide the maximum 3 buoyancy consonant with shatter-resistance of the body for the quantities of materials used.

For a better understanding of the nature of this invention and the manner in which it is constructed, reference should be had to the following description; and the accompanying draw ing, wherein:

Fig. 1 is aperspective view of a flotation body according to this invention in the form of a block-g;

which is suitable for floating heavy ,equiprnept lo such as military trucks and tanks when a plun rality of these blocks are afiixed thereto;

Fig. 2 is a central sectional view=pf a block 1,913.31 as that shown in Fig. 1 wherein theicore=osex panded polystyrene resin is in the for-m or. a. single block; and

Fig. 3 is a central sectional view similar to Fig. 2 of a modified form of flotation bod-yiaecording to this invention wherein the core of polysty n-i io mee of a rl ralit -o ieqret blocks.

Referrin n wto h aw .na; i r i ewn fl t nb yaecerdi gtoth nt en mall-he facturednsubstantiflilly in ;-the.-shape. ;of a cube which: isziadap'ted wh nafii d to e rrieee of military equipment to help ;fioat; the equipmentwhen it :is; .inm ersed in water To float ieuuipmentlgsuch asatrucl a plurality pf ;-these b1QCk5-,;WQI;L1C1gbBy-fiXBd to the truck about the sameioy. sui a le fi inees utr nc these fittin s and the manner ofattaching-them to the. equip ment fo rm;-;no, part of thi s invention andsince m y uitable means-fo perfqrming these functionsgwill readily occur to those skilled in these matters they have not been illustrated-in the drawing... The .flotatien body- ,according to this inventionshown in the drawing consists of a block Ail comprising v a relatively large core .ll of expanded cellular po tyren r s n eh erempletely. enclosed in a relativ ely thin shell of ,a toughrather rigid expanded cellular .material. I the.. mhedim te e ni- Fi 1 an lit e cored- 1 :i thei rm of a in le bl k t-l pend d-mohair en them 1 h" @959 sh e 12 .which ha e beenieformecl t a su tab e s a e. n -p ace a ou hel e st re ewere; he S e s, 4 2 met beibenciefi teeache h i t e a eas 1 where her' v flae al i erma unitary a qnb ng rreiemh rv he yma p e d to ach. o h nd to the-polystyrene lcore 1| ere-the slabsabut against this il-1 i i s. re:

ne ne.me i fi da ete ie oc I ti Fig: 3, thepore comprises .a plurality of. polystyrene blocks; A l which. .are spaced apart .by sheetsor slabs iz of the shell material interposed lie tween the blocks ll These. blocks H and sheets 12 are suitably shaped so that a core aybe. a embled th m e with rithut-adher n t e. sheet t -b ck as eairedswh ehl Q e ma .b e os d i a sh l oe-tne teee .4 z i hes me m n a n' h e e-z-i w med astl s e b k feel s rren 8.

In; formingrthe flotation bodies accordingto is. invention! t e x n e a p ly tyr n cores II, II may be .madeby the following technique g id r lysty e e Sin pu ve z d form.

agas suchas methyl chloride areheatedin a clpsed vessel-under.,a pressure at about 30. atmos rheres to-a temperature above the .fusion ause.ahsqr enreie e e sjb ither ymerd.

75 Barton 2,484,397. This plastisol is'then confined valve is then opened in the bottom oi the vessel to permit flow of the polymer therefrom. Dur ing flow from the vessel, the polymer is swollen by expansion of the gas and is caused to as-- sume the form of a somewhat elastic non-brittle cellular body composed for the most part of individual ,closed cells. The. heated .polymer may bedis h r edei em ey s w ito en air or into another vessel to shape the expanded polystyrene stock. The expanded polystyrene stock may beshaped in the configuration of a core ,1 I pur ing this-expanding operation, or it may be formed as a larger mass from which one or more cores may be severed a separate operation.

To formtthe, ojugh rather rigid shell, suitable 15 -.=plas'tic-..-.materia S. .are compounded as described hereinafter andexpanded by a similar process to form sheets or slabs suitable for covering the corenoiy polystyrene resin. This shell material similarly may be manufactured in the ultimate shape,of,.the .slabs 12 .during expansion of the material, or larger masses may be manufactured from; whichthe sheets]? of appropriate size and thickness are subsequently severed.

'The tQughrathe .rig'id shell is made from an expanded materialselected from the group consisting .of; ,plas'ticized polyvinyl chloride, plastici zed resinous copolymers of a major proportion of vinyl chloride and a minor proportion of a copolymerizablemonomer, and mixtures 'Of (A) figoni,'50..to -80 per cent of -a thermoplastic resin and .(B' correspondinglyfrom '50 to 20 per cent of,a;.r lb.bery material compatible with this resin. For example, expanded. cellular polyvinyl resin stocks suitable for. this shell material may be formed of polyvinyl chlorideor .of a coploymer of vinyhchloride, and yinyl acetate, or of a copolymenp v n hlo d a t ylma e To produces. shelljh ing the toughness'and other aby mal pheraateristie re u si e. in the flotation body shell or this invention, these polyvinyl resins are ,notused alone, but they are p'lasticized with a suit able,plasticizer A liquid plasticizer such as,d'ioctyl-phthalatemay be used, in whichcase frprn 15 'tof30parts by weight per 100 parts of resin are mixed "with the resin to form the shell StQQkAOI solidplasticizers such as dicyclohexyl permea i hny p r'hq at or p n ,pl ithalate may'be used, 'in which'case '50 or slight- 'ly. more partsjbyy/eight are mixed with the resin .ltolforma shell material which when combined with thepolystyrene .core produces a shatter-retantflqtatio body. he li p st e zers may h ne d. i re ter; pr portion t n t qu plasticizers because, the. former are not as drastic theirf eit i n iee r-t e resins as theli uid :p1astieizedre in. eta s itable b ow a ent. The

preferred. :blowine ag nt; for this purpose is dinitroso penta methylene tetramine,;.butoth e rs .suchras'ad-iazoaminobenzene,.:p,pfwoxybis (benzene -sulfonylnhydraaide). or alpha,.. alphaiw-azobisisobutyronitrilesmay..besnseda As. is customary, a

small-quantity {Grime 2 to .5 parts floy weight per lilo-partsofnmplasticized resin) rot-Ma suitable heat or iightstabilizer-sueh; as calcium stearate is; added to the mix.

ln compounding the polyvinyl resins, if -a aeid la ticizeri used a as sel m be iqrmed heinere i l taiby.; Chn Q ..W ik w t e nlas iea tee eru x mrle. e pat nt to in a mold under pressure and subjected toheat in a manner similar to that taught by the patent to Cuthbertson to cause the resin to dissolve in the plasticizer and to decompose the blowing agent. The material is then removed from the mold and subjected to heat to expand it to its final shape. When a solid plasticizer is used, the materials may be mixed on a mill by techniques well known in the plastics art, and the gas liberated from the blowing agent and the mix subsequently'expanded in the same way as when a liquid plasticizer is used. An additional advantage is achieved in a polyvinyl resin shell when solid plasticizers are used, for these plasticizers do not escape as readily upon aging as dothe liquid plasticizers. A further example of a material suitable for the tough shell is one formed of a mixture of a thermoplastic resin and a rubbery material compatible with this resin. A satisfactory mixture maybe formed of from 50 to 80 per cent of a hard inelastic resinous copolymer of butadiene and styrene and correspondingly from 50 to 20 per cent of GR-S. Such a mixture containing 30 percent of GR-S and 70 per cent of the resinous copolymer of butadiene and styrene (these ingredients being mixed with suitable quantities of zinc oxide, sulfur, an accelerator and an antioxidant as is usual in such mixtures) would be suitable for the shell material. This material similarly is mixed with from to 40 parts by weight per 100 parts-of the resin-rubber mixture of a suitable blowing agent such as those speci fied above to provide an ultimate expanded cellular material having the requisite low density,

merizable monomer-and a rubbery coploymer of butadiene and acrylonitrile in proportions of from "50 to 80 per cent oi -the former and correspond- 'inglyfrom 50 to per cent of the rubbery co- "polymerw- Still a further example of a mixture of a thermoplastic resin and a rubbery material compatible with this resin which is suitable for the tough shell of the flotation body according to this invention, and the material which is preferred for this tough shell, is a mixture of a resinous copolymer of styrene and acrylonitrile and a rubbery copolymer of butadiene and acrylonitrile as disclosed in the Daly Patent 2,439,202. These materials may be mixed in the proportions of from 50 to 80 per cent of the resinous coploymer of styrene and acrylonitrile and correspondingly from 50 to 20 per cent of the rubbery copolymer of butadiene and acrylonitrile to provide a shell which when combined with the polystyrene core will produce a flotation body having the requisite shatter-resistance, and a preferred mixture for this shell is one containing from 50 to 70 per cent by weight of the resinous copolymer oi styrene and acrylonitrile and correspondingly from 50- to per cent of the rubbery copolymer of butadiene and acrylonitrile. This mixture is similarly compounded with from 15 to 40 parts by weight per 100 parts of the resin-rubber mixture of a suitable blowing agent to produce an ultimate expanded material having the requisite density for the flotation body.

A more specific example of this preferred mixdensities.

, 6" tu'r "rorthe" shell material, "and the manner of producing it is as follows Parts Styrene-acrylonitrile. resin (-15) 6 5 Copolymer butadiene-acrylonitrile rubber." 35

, The styrene-acrylonitrile resin and the Buna N rubber are charged into a Banbury mixer and masticated for 10-15 minutes at 320 F. All of the remaining ingredients except the blowing agent and the sulfunare added and mixed with the rubber and resin until a homogeneous mixture results. The stock is then discharged from the Banbury and sheeted out. It is then banded on a rubber mixing mill where the sulfur and blowing agent are added without permitting the temperature of the stock to exceed 200 F. g

If a smooth finish is desired on the final molded cellular material, the stock is calendered before molding. The composition is then converted into cellular blocks in accordance with the Cuthbertson process. The first step, which comprises molding under pressure without permitting any expansion, is carried out at 285 F. for .20 minutes. The stock is cooled before releasing from the mold. This slab is then expanded freely in space or in a larger mold for 45 minutes at 340 F. The density of the final product is' controlled by the amount of expansion that is permitted. To obtain adensity of 5#/cu. ft. or less, it is preferred to permit the material to expand to its maximum volume. r g e A rather large proportion ,of,blow ing agent (from 15 to 40 parts by'weight) isused toexpand the plastic materials making up the flotation block according to this invention because it is necessary to expand the materials to low Preferably when used as an equipment float the density of the flotation body does not exceed 5 lbssper cubic foot, for when the density gets much above this figure the bodies are not too satisfactory for floating heavy equipment such as amilitary, truck or tank. A preferred flotation body for this purpose would have a density in the range of 4.75 to 5 lbs. per cubic foot.

Flotation bodies constructed in accordance with this invention having a relatively thin shell and a relatively large core are capable of withstanding gun fire without shattering or crumbling. Thus a body having over-all dimensions on the order of 2 to 5 feet and having a shell of 1 to 4" in thickness, when subjected to gun fire from a .50 calibre machine gun will be pierced by a hole along the path of the shell. Larger calibre shells which do not tumble would leave a similar hole. In contrast with this performance, a cellular polystyrene flotation body will be blown to dust by such gun fire.

It will be evident from the foregoing that by utilizing this invention, a superior flotation body of great buoyancy can be produced, and that a. tough and durable fiotation body suitable for varied uses under extreme adverse conditions will be formed.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A buoyant flotation body comprising in combination a core of expanded cellular polysty- 7r rene resin-and .a shell sham-the core formed of: an expanded cellular l fiiifitlzhslg ifidc lfq illiii h group consisting of plasticized polyvinyl chloride, .plasticized; resinous.:c nolymi1t-ofiauma ioli proportion .of .yinyl, chloride and a minorpropor tion of a copolymerizable;monomerrandmixtures cized resinouscopolymers of 1 a major. proportion 1 of vinyl chlorideand aminor proportion of-ra copolymerizablemonomer, and mixtures :of (A) from 50 to '70 per cent of a thermoplastic resin and H3) correspondingly from -50 to .30..per cent of-a rubbery-material -compatible' with :said resin.

3. 1 5. flotation body adaptedto float.=-heavy equipment in -waten when :fixed theretorcomprising incomhination a ==core-of= expanded cellular polystyrene resin and a shell having .a thickness in the range of- 1 to 4 inches completely (.S'LH'. Y

rounding -said core and -bonded thereto, said shell' 'beingformed of-a tough ex-pandedcellular material selectedfrom the group consisting :of plasticized polyvinylchloride; pla'sticized resinous copoly-mers of-a major proportion oflvinylwchloride and -a minor proportion -of--a copolymerizable monomer, -and mixtures of (A). from 550- :tov 80 per cent of a thermoplastic resin and .(Bhcorrspondinglyirom -50--to Ell-pen cent ofa rubbery material compatible with said resin:

4.- A flotation "block comprising in combination a core-of-expanded-cellular polystyrene resin and a relatively-thin shell of-a ztoug h expanded cellula-r material bonded-to thencore said shell zbeing thermoplastic -resin and correspondingly 1 from Sa to 20' per cent-of a rubber-y --materia1: com- 'patilole 'with said resint 5. A fiotationbodyadapted to maintain heavy bodies- --afloat in water whenattaehed: thereto cemrr s neca core for expanded ..ce1lular. po y: styrene re in and a shell oitou hexpandedoelluw lar1-.+materia1, said. shdlhavine a thi kness in theran of 1 .t 4 inches, said shell-being formed of: ;aqmi,xtur,e;0f;-50 .to ,70 per centof .a resinous copolyr ner oi styrene and. acrylonitrile and cor-v responding-1y .fr om.5o to. 30. per ,cent ofv a rubbery copolymer of butadiene and. acrylonitrile.-

6.1; A notation bo y. having a density notgreater than -fa pounds per cubiofoot, said body com.- pri-sing in combination a core of expandedcellul crrrpolystyreneresin and/a .shell .of expanded cellular: material completely enclosingsaid core, saidzshellhavinga thickness in .therange-of 1 tore inches, said shellbeing formed of amixture of from 50 to 70 per cent of a resinous oopolymer of styrene and acrylonitrile and correspondingly from 50. .to, .30 per centof .a rubbery copolymer ofbutadiene and acrylonitrilen 7. 1A.:non-sha-tter-ing fiotationbody comprising incombin'ationa core of expanded cellular polystyrene resin,- a shellof, expanded-cellular material, surrounding said core, and bonded thereto, saidshellbeing formed of a plasticized poly vinyl resin;-and ,havinga thicknessmthe range of. 1 to 4 inches, said flotation body havinga densityhnot greater than -5 pounds per cubic foot.

8. A.flotation ,body;according to claim 7 in which, said shelll-is formed of vplasticized polyvinyl chloride.

9.. A fiotation body. accordingto claim 7 in which said she1l1is .formedof .a plasticized copolymer of vinyl chloride and vinyl acetate.

10.. A flotation :body ;ac,cording to claim '7 in which saidshell is.;formedof1a-plasticized c0- polymer of vinyl chloride and ;diethyl maleate.

References Cited in'the file of this patent UNITED. STATES, PATENTS Number Name Date 1,466,671" Morin. r ,.p. Sept.- 4, .1923 1,930,441.; lvlillerr r v r Oct. 10, 1933 2,439,202 Dalyn" Apr.- 6,1948 2,448,056.. Cooper.; Aug. 1'7, 1948 2,448,154 Richmond Aug. 31,1948 2,526,311. Wilson Oct. 17,1950 2,532,242. Ott Nor/".28, 1950 Pfleumer.;- r Feb. '6, 195.1 

4. A FLOTATION BLOCK COMPRISING IN COMBINATION A CORE OF EXPANDED CELLULAR POLYSTYRENE RESIN AND A RELATIVELY THIN SHELL OF A TOUGH EXPANDED CELLULAR MATERIAL BONDED TO THE CORE, SAID SHELL BEING FORMED OF A MIXTURE OF 50 TO 80 PER CENT OF A THERMOPLASTIC RESIN AND CORRESPONDINGLY FROM 50 TO 20 PER CENT OF A RUBBERY MATERIAL COMPATIBLE WITH SAID RESIN. 